Vapor sensing devices using a surface acoustic wave (SAW) sensor are known. See for example U.S. Pat. Nos. 5,469,369, and 5,465,608 incorporated herein by this reference.
Such devices can be used in systems to detect the presence of a contaminant (e.g., fuel, moisture, or a coolant) in oil (e.g., engine oil, hydraulic oil, or the like). The fuel dilution meter (Q600) product available from Spectro Scientific, Inc. (Chelmsford, Mass.) is an example of such a system.
In that system, a rather large bottle is filled % full with oil and inserted into the machine. A tube is inserted into the bottle. Vapors in the “headspace” of the bottle above the oil are drawn via the tube and a pump over a SAW sensor module which detects the presence of contaminant vapors.
But, if the bottle is filled too full, liquid oil can be drawn into the instrument and damage the SAW sensor. Also, oil can contaminate the tube, the vapor inlet, the sample stand, and/or other components of the system resulting in erroneous readings.
Finally, this test method is very sensitive to oil temperature under test. Due to the high oil volume it takes a long time to cool down the oil sample if oil was freshly collected from a warm or hot engine. Error occurs when sample is not tested at the same temperature as the calibration samples are tested.
Moreover, the current system is not portable and requires the sample to be delivered to a laboratory for analysis.